1. Field of the Invention
The present invention is directed to furnace and boiler stoker devices, and more particularly to an improved coal feed mechanism and control system for automatically regulating the amount of a fuel such as coal being fed to a furnace fire bed.
2. Preliminary Discussion and Discussion of Prior Art
With the price of fuels such as oil and gas continuing to rise, stoves and furnaces that use other less expensive fuels such as coal are becoming increasingly popular. Most coal stoves and furnaces include some type of stoker device or system for automatically feeding coal into the stove or furnace as needed. One such prior art device is described in U.S. Pat. No. 4,537,140 issued to Baker entitled “Automatic Coal Stove Stoker”. FIG. 1 is a sectional view of the prior art Baker mechanical coal feeding mechanism, and shows a fire box in communication with a coal hopper in a usual manner, with the hopper floor sloping downwardly toward the fire box where it abuts against a similarly angled downwardly sloping perforated fire grate, so that coal in the hopper is caused by the force of gravity to slide or roll down the hopper floor through a restricted exit passage in the hopper onto the grate. In addition, as part of Baker's coal feed mechanism a linearly reciprocating slidable plate is provided on the floor of the coal hopper, which aids in advancing coal out of the hopper onto the grate. In effect, the reciprocating motion of the plate on the hopper floor in Baker enhances the gravity flow of coal out of the hopper. Such plate is operably connected to a motor via an eccentric movement means and a rod that extends through an aperture in a downwardly depending shoulder on the upper edge of the plate, which shoulder serves as a pusher bar. An end stop and a threadably adjustable stop are strategically positioned on the rod on opposite sides of the shoulder, so that movement of the rod by the eccentric movement means cause the plate to essentially be pushed back and forth in a reciprocating linear path on the hopper floor as the stops on the rod alternatingly engage against either the outer and inner sides of plate, respectively, with a pause in sliding movement for the duration of rod movement between the two stops. As the plate is urged rearwardly by the inner stop, coal in the hopper falls downwardly onto the floor of the grate into the space vacated by the front of the plate, so that when the plate is moved forwardly again the leading edge of the plate pushes or forces such coal out of the hopper into the fire box and grate. A fan to affect a forced draft upwardly through the grate to enhance burning is also provided.
While the Baker coal feed mechanism is suitable for its particular purposes, a drawback is that although the reciprocating plate stroke length can be varied to regulate at least somewhat the amount of coal being pushed into the fire box, and therefore the amount of heat produced, in order to adjust the linear distance the reciprocating plate moves, the position of the adjustable stop must be manually rotated either clockwise or counterclockwise on the threaded rod. Such manual adjustment procedure is limiting as well as inconvenient in today's modern society, since, for example, a homeowner may wish to decrease the amount of heat generated during daytime hours when no one is home, and then automatically increase the heat during morning or evening hours, which is not possible where only manual adjustment is achievable. Further, in order for a stoker-fed coal furnace to operate properly, there must be a sufficient fire in the furnace at all times to ensure combustion of the additional coal supplied by the stoker. It is known in other prior art coal stoker arrangements to additionally provide a thermostat or other temperature sensing device to automatically turn the power to the stoker motor on and off, thereby regulating the amount of coal burned and heat generated. A thermostat can also be used to activate the stoker at sufficiently short intervals to ensure that additional fuel will be called for before the fire has reached so low a level as not to be capable of igniting the fresh fuel. However, this frequently does not provide for sufficient regulation of room temperature, and is generally undesirable and ineffective particularly for relatively single stoker systems for coal stove-type devices and the like.
The present inventor, recognizing the limitations inherent in previous coal stoker equipment, has devised a surprisingly efficient and effective arrangement for periodically adjusting or regulating the distance a linearly reciprocating plate such as those used in the Baker type stoker feeding mechanisms travels, which provides significantly improved thermostatic control of the amount of fuel that is forced into the fire box and also as a result the temperature of a room or interior building space. The present invention can also be used with other types of mechanical stoker systems wherein a mechanical reciprocating pusher is utilized. For example, U.S. Pat. No. 4,662,290 issued to Potts entitled “Automatic Coal Stoker” discloses a pusher assembly having a slidingly reciprocating rectangular box configuration with a cam inside, wherein rotation of a cam imparts a reciprocal sliding motion to a pusher assembly. The present invention can also be used to automatically regulate the operation of the Potts coal stoker, rather than having to manually turn the stroke adjusting screw or change the size of the cam. U.S. Pat. No. 6,647,091 issued to Somers entitled “Automatic Coal Stoker” is an example of another similar assembly but having a substantially horizontal fire grate with which the present invention can also be utilized.